Gemstone with a chaton cut

ABSTRACT

Gemstone with a chaton cut, in which tapering facets of a crown adjoin a flat table all the way round inclined relative to the table, the said facets extending as far as a rondist at which the gemstone has the largest transverse dimension, wherein a pavilion of facets preferably terminating at a point adjoins below the rondist, and wherein the gemstone is at least partially made of glass, and wherein the crown angle (α) is between 40.5° and 42.5°.

The invention relates to a gemstone with a chaton cut.

In order to improve the brilliance and other optical properties of a facetted cut gemstone, over the course of time many different cuts have been developed that differ on the one hand by the number of facets and on the other hand by the mutual geometrical positional relationships of the facets.

In particular for the chaton sector the so-called oktant or xilion cut (e.g. Swarovski stones A1200 and A1028) has in the past become established in the market, since these cuts are considered to be aesthetically pleasing and can be satisfactorily reproduced.

Important parameters for the evaluation of a gemstone are the so-called “fire” and “light return”, which is based on the numerous internal light reflections. These light reflections are produced at the individual facets, which are in special angular relationships to one another characterising the respective cut. The cut and the material of a gemstone are thus decisive for the resultant fire and light return.

The light return value specifies how much light from a predefined solid angle range that is incident on the gemstone is directed back to the observer in a relatively narrow (aperture angle 3°) solid angle range substantially along the axis of symmetry of the stone.

A further important feature for evaluating the brilliance of a gemstone is the fire. Fire denotes the property of a gemstone to split the incident white light into its spectral components. The expression of this property depends on the material (dispersion) and also on the cut.

A gemstone with a chaton cut has a crown, also termed upper part, with a defined number of side facets and a middle flat table, as well as a pavilion, also termed lower part, with a defined number of facets. The end of the gemstone remote from the table can be formed as a point or as a rounded point in the form of a so-called culet. A so-called rondist (circumferential edge) can be arranged between the upper part and lower part. The gemstone can be cut symmetrically or asymmetrically.

The object of the invention is to further improve the aesthetic impression of a gemstone with a chaton cut by optimizing the optical parameters, in particular the fire and light return.

This is achieved by a gemstone having the features of claims 1.

On account of the fact that the gemstone has a chaton cut, in which the crown angle (α) is between 40.5° and 42.5°, this surprisingly produces a particularly high light return with at the same time a high fire. The scintillation (sparkling effect that occurs on moving the gemstone) and the brilliance of the gemstone are exhibited extremely effectively.

The crown angle is that angle which in a side view of the gemstone is enclosed between the lateral boundary line of the crown and the rondist plane, this boundary line being generated by an orthogonal projection of a crown facet onto a plane containing the longitudinal axis of the gemstone.

The rondist plane is that plane which is arranged parallel to the table and in which the gemstone has the largest cross-sectional dimension. The rondist plane is aligned perpendicular to the longitudinal direction of the gemstone.

The light return and the fire can be measured, as is described further hereinbelow for example with the aid of FIGS. 5 and 6. Instead of an actual measurement the measurement can also be computationally simulated on the basis of the geometry and material of the gemstone.

Further advantageous modifications of the invention are defined in the dependent claims.

It has been found that particularly preferred crown angle ranges (α) lie between 41.75° and 42.25°. The crown angle (α) is most particularly preferably 41.95°.

In a preferred embodiment of the invention the pavilion angle (β) is between 39.5° and 41.5°, preferably between 40.5° and 41.0° and most particularly preferably is 40.73°.

The pavilion angle is that angle which in a side view of the gemstone is enclosed between the lateral boundary line of the pavilion and the rondist plane, this boundary line being generated by an orthogonal projection of a pavilion facet onto a plane containing the longitudinal axis of the gemstone.

Although the gemstone according to the invention may preferably be made of a glass, a gemstone of natural or synthetic precious or semi-precious stone or synthetic material with the chaton cut according to the invention is also possible.

The crown of the gemstone, which is also known as the upper part, has a table on which eight crown facets adjoin in each case via a broad side. In one embodiment of the invention the angle between these crown facets and the rondist plane is between 33.5° and 35.5°, (preferably between 34.25° and 34.75° and most particularly preferably is 34.52°).

In addition the crown has eight further crown facets, which in each case adjoin the rondist via a broad side. In one embodiment of the invention the angle between these crown facets and the rondist plane is between 40.5° and 42.5° (preferably between 41.75° and 42.25° and most particularly preferably is 41.95°). The orthogonal projection of the last-mentioned crown facets generates the crown angle.

The pavilion, also known as the lower part, has at least 16 pavilion facets, which terminate in the form of a point or a culet on the end remote from the table. In this manner, in one embodiment eight pavilion facets have a point that is arranged in the direction of the rondist, while eight pavilion facets have a broad side that is adjacent to the rondist. The end of this pavilion facet remote from the broad side terminates in a point and is directed away from the rondist. These pavilion facets adjoining the rondist via the broad side have in one embodiment an angle between 39.5° and 41.5° relative to the rondist plane, preferably between 40.5° and 41° and most particularly preferably 40.73°. The orthogonal projection of the last-mentioned pavilion facets generates the pavilion angle.

In one embodiment of the invention the angle between the rondist plane and those pavilion facets that have a point adjoining the rondist or that is arranged in the direction of the rondist, is between 35.0° and 37.0° (preferably between 36.0° and 36.5°, and most particularly preferably is 36.28°.

Further details and advantages of the present invention are described in more detail hereinafter with the aid of the description of the figures and with reference to the drawings, in which:

FIGS. 1 a to 1 c are respectively a side view, a plan view and a view from below of a gemstone according to the invention,

FIG. 2 is a schematic representation of the definition of the crown angle and pavilion angle,

FIGS. 3 a and 3 b compare respectively a gemstone of the prior art (Swarovski A1200) and a gemstone according to the invention by means of a schematic representation of ray paths.

FIG. 4 is a light return/fire diagram

FIG. 5 is a schematic representation of the measurement arrangement for measuring the light return

FIG. 6 is a schematic representation of the measurement arrangement for measuring the fire

FIGS. 7 a to 7 c show a further embodiment of a gemstone according to the invention in a side view.

FIG. 1 a shows a gemstone 1 according to the invention in a side view. The rondist 4, which separates the crown 2, also termed upper part, from the pavilion 3, also termed lower part, can be recognized. The rondist 4 is that region of the largest cross-sectional dimension of the gemstone 1. The symmetry axis (longitudinal axis L) of the gemstone is also schematically illustrated.

The pavilion 3 has two types of pavilion facets 8, 9 (two-layer cut). In this case eight pavilion facets 9 have a broad side via which they adjoin the rondist 4. The remaining pavilion facets 8 have a point that in each case adjoins the rondist 4.

The crown 2 also has 16 facets 10 and 11, as well as a flat table 5, which is aligned parallel to the rondist plane 7 and perpendicular to the longitudinal axis L.

Eight crown facets 11 adjoin the rondist in each case via a broad side and have a point that is aligned in the direction of the table 5. Eight further crown facets 10 adjoin the table 5 in each case via a broad side (two-layer cut).

FIG. 1 b shows a plan view of the crown 2 of the gemstone 1. The symmetry of the gemstone 1 can be recognized by the schematically illustrated coordinate cross on the table 5. The longitudinal axis L runs through the centre of the coordinate cross.

FIG. 1 c shows a view from below of the pavilion 3 of the gemstone 1. A further coordinate cross to illustrate the symmetry of the gemstone 1 is symbolically shown at the point 6, which is formed by the mutually adjoining pavilion facets 8.

FIG. 2 shows a schematic representation to illustrate the crown angle α, which is formed between the rondist plane 7 and the lateral boundary line 16 of the crown 2, while the pavilion angle β is formed between the lateral boundary line 17 of the pavilion 3 and the rondist plane 7.

FIG. 3 a shows a gemstone 1′ with a chaton cut of the prior art (Swarovski A1200). The light rays 13 entering the gemstone are only partially reflected back in the direction of view at the pavilion 3′ on account of the angle with which the pavilion facets are cut, in particular on account of the crown angle and the pavilion angle. A proportion of the rays is refracted laterally or is scattered in the form of the ray 14. The light return value is reduced.

FIG. 3 c shows the same representation for a gemstone 1 according to the invention. On account of the special geometrical arrangement of the different facets and of the crown angle α and pavilion angle β, the light return is significantly improved, since the majority of the rays are totally reflected in the region of the pavilion 3, so that virtually all the light rays 13 entering the crown 2 are reflected back to the observer, after possibly undergoing multiple reflection, in the form of light rays 15 leaving the crown 2.

The following table shows the differences of the known gemstone A1200 of the applicant according to the prior art, compared to a gemstone “1021” according to an embodiment of the invention.

FIG. 4 shows the position of this gemstone 1021 according to the invention in the so-called light return/fire diagram. It can be seen that the gemstone according to the invention has simultaneously high light return values and high fire values compared to the prior art A1200 and A1028, which is another gemstone of the applicant, and is thus superior to the prior art as regards the optical properties and the aesthetic impression. FIG. 5 shows in a schematic view a measurement arrangement for measuring the light return of a gemstone. A gemstone 1 arranged in the centre of the base circle 17 of the hemisphere 16 is illuminated by light rays 18 from a hemispherical illumination arrangement 16, so that the crown 2 of the gemstone 1 is illuminated with white, diffuse light, the light rays hemispherically striking the gemstone 1 at a blacked-out region 19 and being reflected from the gemstone. The base circle 17 is blacked out except for a recess for the gemstone 1, so that no light is incident on the gemstone 1 from underneath the base circle 17. A region 19 of the hemisphere 16, which lies directly opposite the gemstone 1 and has an aperture angle □ of 46°, is likewise blacked out. From this region too no light is incident on the gemstone 1. The region 19 has a recess 20 with an aperture angle □ of 3°. This recess 20 serves as a narrow measurement field for a detector. A detector measuring a stream of light can thus be arranged above the recess 20.

Instead of this arrangement, the respective light-specific values, such as for example the brightness in the region of this recess 20, can be calculated in a computer simulation.

The amount of light reflected upwardly from the gemstone 1 represents a mean value over almost all possible illumination arrangements and thus provides a quantitative measure for the light return of the gemstone 1. The reflections take place at different facets, so that light is reflected back to the recess directly on first striking the gemstone, but also after multiple internal reflections.

FIG. 6 shows a measurement arrangement for the fire value. The gemstone 1 held by a holder 20 is illuminated through the opening 22 in the direction of its main axis with a directed beam from the light source 21. The back-scattered light from the gemstone 1 is recorded in color on a measurement field 24. The product values from the saturation and illumination intensity of the light points collected in the measurement field 25 are summated and thus give the numerical value for the fire.

FIGS. 7 a to 7 c show in a schematic side view a gemstone according to a further embodiment of the invention, similar to FIG. 1 a, though in this case the stone in contrast to the stone of FIG. 1 a has a pronounced circumferential edge 4 a (rondist), which in plan view encircles the gemstone.

The invention is obviously not restricted to the illustrated embodiments, and in particular the number of facets can vary, in contrast to the illustrated gemstone, which has in each case 8+ facets on both the table and pavilion, though other combinations of facets can also be employed, for example 6+6, 10+10 or 12+12 facets. Odd numbers of facets are also possible. Also, the number of facets between the crown on the one hand and pavilion on the other hand do not have to match.

In the illustrated embodiment the crown as well as the pavilion contains two different cutting angles (two-layer cut). In principle single-layer and multiple layer gemstones are also possible.

Glass is used as preferred material, preferably with a refractive index between 1.50 and 1.60, and most preferably 1.55. Other materials, in particular natural stones, are however also feasible and possible. 

1. Gemstone with a chaton cut, in which tapering facets of a crown adjoin a flat table all the way round inclined relative to the table, the said facets extending as far as a rondist at which the gemstone has the largest transverse dimension, wherein a pavilion of facets preferably terminating at a point adjoins below the rondist, and wherein the gemstone is at least partially made of glass, characterized in that the crown angle (α) is between 40.5° and 42.5°.
 2. Gemstone according to claim 1, characterized in that the crown angle (α) is between 41.75° and 42.25°.
 3. Gemstone according to claim 2, characterized in that the crown angle (α) is 41.95°
 4. Gemstone according to claim 1, characterized in that the pavilion angle (β) is between 39.5° and 41.5°.
 5. Gemstone according to claim 4, characterized in that the pavilion angle (β) is between 40.5° and 41°.
 6. Gemstone according to claim 5, characterized in that the pavilion angle (β) is 40.73°.
 7. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those crown facets (10) that adjoin the table (5) via a broad side, is between 33.5° and 35.5°.
 8. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those crown facets (10) that adjoin the table (5) via a broad side, is between 34.25° and 34.75°.
 9. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those crown facets (10) that adjoin the table (5) via a broad side is 34.52°.
 10. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those crown facets (11) that adjoin the rondist (4) via a broad side is between 40.5° and 42.5°.
 11. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those crown facets (11) that adjoin the rondist (4) via a broad side is between 41.75° and 42.25°.
 12. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those crown facets (11) that adjoin the rondist (4) via a broad side is 41.95°.
 13. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those pavilion facets (8) that have a point that is arranged in the direction of the rondist (4) is between 35.0° and 37.0°.
 14. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those pavilion facets (8) that have a point that is arranged in the direction of the rondist (4) is between 36.0° and 36.5°.
 15. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those pavilion facets (8) that have a point that is arranged in the direction of the rondist (4) is 36.28°.
 16. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those pavilion facets (9) that adjoin the rondist (4) via a broad side is between 39.5° and 41.5°.
 17. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those pavilion facets (9) that adjoin the rondist (4) via a broad side is between 40.5° and 41.0°.
 18. Gemstone according to claim 1, characterized in that the angle between the rondist plane (7) and those pavilion facets (9) that adjoin the rondist (4) via a broad side is 40.73°.
 19. Gemstone according to claim 1, characterized in that the transparent material of the gemstone has a refractive index of 1.50 to 1.60.
 20. Gemstone according to claim 1, characterized in that the transparent material of the gemstone has a refractive index of about 1.55.
 21. Gemstone according to claim 1, characterized in that it is predominantly or entirely made of glass. 